The present invention relates generally to the field of printed wiring boards and, more particularly, to mechanical stiffener apparatus and methods for rigidifying printed circuit boards.
Modern high performance computers contain a number of printed circuit boards (PCB) to carry and interconnect the various integrated circuit chips and other components that make up the computer system. Computers may be configured to have one or more subsystems, each in its own right a computer, that are interconnected into a larger, greater capacity computer. Each subsystem may contain basically the same components assembled in a chassis. Within a given subsystem, there may be, among others, a processor board, a power board, and any number of secondary or daughter boards that are carried upon a support structure within the subsystem chassis. These subsystems of boards are carried in racks in the computer chassis.
Processor boards are so named as they have attached to them one or more processors, or central processing units (CPU). The CPU is an integrated circuit (IC) chip that is considered the xe2x80x9cbrainsxe2x80x9d of the computer. The processor board serves as a communication medium for the exchange of electrical signals among the one or more attached processors and other electrical components attached to the processor boards, daughter cards, and other components. The processor board itself is sometimes referred to as a backplane, mother board, system board, or mainboard, depending on its function and configuration.
The processor board is a printed circuit board. A PCB is a relatively thin, flat sheet structure. The PCB may be made of laminations of reinforced fiberglass or plastic and metallic interconnects which electrically link the components attached to the board. As flat sheets, PCBs are subject to bending and flexing stresses depending on the weight of the attached components and the method used to attach the PCB to the chassis.
Some state of the art processors are an assembly consisting of a processor module and a power conditioning module with attached heatsink. These assemblies are relatively large and heavy, wherein the structural integrity of the PCB comes into question. The localized weight of the processor assembly, combined with the combined weight of the other components assembled onto the processor board, requires that the PCB be able to support handling, assembly and other stresses within acceptable limits of flexure without compromising the structural integrity of the PCB. Excessive loading will have a detrimental effect on the integrity of the electrical component interconnects and may result in failure of the electrical system.
To mitigate the effects of deflection, support structures for resisting longitudinal and lateral flexing have been attached to PCBs. A processor board is commonly supported to some degree by the mounting bolts used for mounting the processor board to the chassis. Supplemental support is sometimes provided by rigidity enhancers laterally or longitudinally disposed across the processor board. These rigidity enhancers have taken various forms.
Common disadvantages with lateral and longitudinal rigidity enhancers include electrical component interference, cooling air flow blockage and deflection, and lack of strength to support a PCB with attached processor assemblies. Improved lateral and longitudinal rigidity enhancers are needed that minimize electrical component interference, minimize the blockage of cooling air flow, and have sufficient strength to support a fully loaded PCB.
Additionally, for a given printed circuit board size, the large processor assemblies take up considerable surface area of the board. In some cases, components which are commonly attached to the PCB are moved to other locations on the board or moved entirely off the board onto daughter boards. As a consequence, the distances between electrical components become large which is detrimental to the performance of the system as a whole.
Processor assembly mounting structures have been used in the art to support the processor module and power conditioner module as an assembly. These structures have taken the form of a frame that supports the outside edge of the processor assembly. The processor module and power conditioner module are electrically connected, and the assembly is mounted onto the frame. Fasteners are used between the frame and the PCB to mount the processor assembly to the PCB. The frames elevate the processor assembly from the surface of the PCB allowing the attachment of additional electrical components onto the PCB surface that would have been covered by the processor assembly if directly attached. The state of the art processor assembly mounting frame requires considerable PCB surface area, limiting the number of electrical components capable of being attached to the PCB.
There is a need in the art for PCB stiffeners and processor assembly mounting apparatus and methods to address the disadvantage of large processors crowding out electrical components on the processor board as well as being able to minimize the bending and flexing stresses on the PCB due to the weight of the processor assemblies and other components.
The above-mentioned disadvantages associated with large and heavy processor assemblies mounted on printed circuit boards, and other disadvantages, are addressed by the present invention and will be understood by reading and studying the following specification.
In particular, the present invention is directed to apparatus and methods for enhancing processor board rigidity by providing processor board stiffeners and processor assembly mounting frames adapted to mount on a processor board surface. The stiffeners and mounting frames resist deflection of the processor board due to the weight of the processor assembly and other components. The mounting frame, additionally, provides accommodation for additional electrical components to be attached to the PCB by elevating the processor assembly off of the PCB, thus providing additional PCB surface area for the attachment of components.
One embodiment in accordance with the present invention includes a mounting frame adapted to attach to the periphery of a component for assembly on to a PCB. The mounting frame is a frame-like structure having external dimensions configured to support an attached electrical component or components. The mounting frame comprises a plurality of legs, a cross leg, a rectangular opening, a partial rectangular opening, a plurality of through-holes, and a plurality of pilot holes. The plurality of legs includes an inwardly extending lip. The inwardly extending lip provides additional support material for supporting the attached components while minimizing the PCB surface area covered by the frame. The mounting frame is relatively thin but rigid. The legs of the mounting frame, in combination with the cross leg, define a rectangular opening and a partial rectangular opening. The partial rectangular opening is adapted to accommodate a component attached to the circuit board. A plurality of pilot holes is provided which are adapted to accommodate mounting means for attachment of the mounting frame to a printed circuit board (PCB). A plurality of through-holes is provided and adapted to accommodate mounting means for attachment of one or more electrical components to the mounting frame.
In an alternative embodiment, the mounting frame is adapted such that the mounting frame peripheral edge substantially conforms to the outer dimensions of the electrical component. The mounting frame peripheral edge overlaps the electrical component bottom surface, such that when the mounting frame is placed against the electrical component bottom surface, the mounting frame rests upon the outer portion of the bottom surface. The fastening means is adapted to make use of the through-holes to fasten the mounting frame to the electrical component.
In one embodiment, the peripheral edge of the electrical component overlaps the perimeter of the mounting frame. In an alternative embodiment, the peripheral edge of the mounting frame overlaps the perimeter of electrical component.
One embodiment in accordance with the present invention includes a truss-like stiffener having external dimensions adapted to support an attached printed circuit board having attached components. The stiffener is relatively thin but rigid. The stiffener comprises a plurality of legs which define a plurality of openings. The stiffener has a fastening surface which is adapted to accommodate a fastening means for fastening to a PCB. The openings are provided such as to not significantly impede the flow of cooling fluid.
In one embodiment in accordance with the present invention, the legs may be formed as an integral unit from a solid sheet of flat stock material. The legs may be formed by, among other methods, machining, cutting, and extruding. In another embodiment, the legs are formed as separate units of stock material and subsequently fastened into the truss-like configuration. The legs may be fastened together by, among other methods, welding, brazing, gluing, and screwing.
In another embodiment in accordance with the present invention, the stiffener is made from a material that is thermally conductive. In this embodiment, the stiffener may be used as part of a heat dissipation system. In another embodiment, the stiffener is made from a material that is electrically conductive. In this embodiment, the stiffener may be used as part of a power or grounding system. In another embodiment, the stiffener is made from an electrically insulative material to minimize electrical shorting.
In one embodiment in accordance with the present invention, stiffeners and mounting frames are used in combination to rigidify the PCB. Two stiffeners are positioned on one side of the PCB, in this example, while the opposite side of the PCB has attached one or more mounting frames. The two stiffeners are positioned perpendicular to the long dimension of the mounting frames. The stiffeners span substantially the width of the PCB.
The present invention reduces the deflection to an acceptable amount in an efficient and economic manner which does not interfere with other electrical components or cooling flow requirements.